[simplicity12]

Hi Everyone,
I was wondering if someone can help explain the following question:
An apparatus consists of three temperature-jacketed 1.000 L bulbs connected by stopcocks. Bulb A contains a mixture of H2O (g), CO2 (g), and N2 (g) at 25'C and a total pressure of 564 mm Hg. Bulb B is empty and is held at a temperature of -70'C. Bulb C is also empty and is held at a temperature of -190'C. The stopcocks are closed, and the volume of the lines connecting the bulbs is zero. CO2 sublimes at -78'C and N2 boils at -196'C.
A. The stopcock between A and B is opened, and the system is allowed to come to equilibrium. The pressure in A and B is now 219 mm Hg. what do bulbs A and B contain?

The answer is:
Bulb A contains CO2 (g) and N2 (g)
Bulb B contains CO2 (g) and N2 (g) and H2O (s).
But I have no idea how they got this. Can anyone help?